STRAP DESIGN & ORDERING TIPS
Customers often come to TAI with a build-to-print copper or graphite thermal strap which they have attempted to design themselves (often times, without a full understanding of thermal strap engineering & design, or strap fabrication limitations and processes). Please note: while we are happy to manufacture a build-to-print strap (if possible), in many cases, if we are not allowed to make minor changes to your design, we will not be able to build your strap (as-is). Because we work with our proprietary GraFlex graphite bundles, pyrolytic graphite and graphene foil sheets, and we use a proprietary cold press assembly technique instead of brazing, welding or soldering our copper rope straps, our design and assembly methods are often quite different from what many engineers are familiar with. As such, it is critical that you contact our experts as early as possible in the process.
Here are a few tips to remember when designing a strap and preparing your RFQ for TAI:
- DESIGNING A THERMAL STRAP YOURSELF DOES NOT REDUCE THE COST OF A PROGRAM: If you are ordering custom copper straps, the price will be the same regardless of the amount of time you have spent trying to design the strap for us (as we still need to include NRE for final drawings, assembly and test fixtures, and machine setup time). All custom straps will include this small NRE/Design Fee. By allowing our engineers to design the strap for you (or to at least participate in the design process where possible), we can optimize performance, flexibility, and minimize mass and impact to your envelope. Further, we always provide front end / notional design and assessment services at no-cost, and we provide programmatic NRE/Design Fee discounts to new customers, universities, and NASA, so you can save thousands on your first custom program.
- DESIGNING A GFTS®, PGL™ or GTL™ YOURSELF WILL JUST COMPLICATE YOUR PROGRAM: TAI developed and optimized flexible GFTS® technology over a span of nearly 23 years (and PGL™ over a span of 6 years), and at a cost of over four million dollars. We understand the very unique material and mechanical properties of our products, and the complexities of their design and fabrication. Attempting to design your own straps (to reduce NRE/Design Costs), will not save you money, and (often) only causes confusion, program and hardware delays, and (often), the potential that no solution can be found (see next tip). We can provide you a free assessment and notional designs in just days, so don't take on the stress of trying this on your own.
- CONTACT US FIRST: And do so before other components, instruments and structural elements are fixed in your application. Our feedback can help to ensure we are provided with the proper geometric envelope and interface areas to meet your performance requirements, and that your strap can be designed and fabricated for optimized flexibility and low cost.
- A FLEXIBLE STRAP IS NOT MADE OF SOLID COPPER OR GRAPHITE/CARBON: One of the biggest mistakes that engineers make is calculating the projected thermal conductance of their proposed design, using the material conductance values of solid OFHC cu and/or graphite. Thus, their anticipated thermal conductance figures are often double what a flexible thermal strap can provide. This does not take into account the resistance losses at each joint/interface, and due to other factors like the number of ropes or sheets stacked next to or on top of, one another.
- FOIL STRAPS ARE STIFF: Understand that a foil strap, whether it is made of copper or aluminum, will be far less flexible than copper rope straps (and carbon sheet straps, while more flexible on two axes, can be catastrophically damaged if flexed on the lateral/Y axis). At TAI, we can build you a foil strap (and our standard series cu foil straps are being released in May of 2018), but we prefer to use OFHC cu rope/cabling when possible. Cabling/rope straps are simply far more flexible (and on each axis), more durable, and cheaper than a foil strap (at about 1/3 - 1/2 the cost of any other competing foil strap). If flexibility, durability, and cost are critical, cabling/rope is your best option.
- THERMAL STRAPS TAKE TIME: What makes our copper thermal straps "standard" are the end fittings. Because every client needs different lengths and bolt patterns (and often needs to customize standard end fittings further), we cannot keep a stock of fabricated straps on hand (sorry, we cannot deliver your straps in a matter of days or a couple of weeks). Custom straps take even longer. Make sure you give yourself a minimum of 4 weeks when ordering standard straps, and 6 when ordering customs (though we can offer expedited delivery depending on the time of year). GFTS® and PGL™ prototype programs take 6-9 weeks, and flight programs can take an additional 4-8 (CuTS® FM programs typically only take 4-6 weeks).